1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor.
In this specification, a semiconductor device means all types of devices which can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
A technique by which transistors are formed using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. The transistor has been applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (also simply referred to as a display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor has been attracting attention.
For example, Patent Document 1 discloses a transistor including a semiconductor thin film formed using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) (In—Ga—Zn—O-based amorphous oxide). In addition, Patent Document 2 discloses a technique by which a transistor similar to that in Patent Document 1 is manufactured and used as a switching element or the like in a pixel of a display device.